In wideband code division multiple access communication (W-CDMA), a User Equipment (UE) employs scrambling and spreading of symbols before being transmitting the symbols to be able to use the same frequency and time domains for different users and different physical channels (PCHs). Hereto, the UE uses a scrambling code assigned by a base station (BS) and applied over a frame of 38400 chips, and a spreading code applied over a number of chips referred to as a spreading factor. In W-CDMA, each frame is divided in 15 slots, each slot is divided in 10 sub-slots and each sub-slot comprises 256 chips. In W-CDMA, the spreading factor is typically 256 for control channels, thus each UE transmits a symbol using 256 chips multiplied with the scrambling code and the spreading code.
The base station may receive multiple reflections of the signal transmitted by the UE with time delays depending on the roundtrip that each reflection has experienced while getting from the UE to the BS. The base station separates these reflections out of the antenna signal from assigning a number of fingers to each UE, with the number of fingers reflecting the number of reflections received in the base station. Hereto, the base station uses a procedure commonly referred to as path search to find the number of reflections and their time offsets. Each finger despreads and descrambles the antenna signal using the spreading code assigned to a PCH and scrambling code assigned to a UE and the respective time offset to obtain, for each finger, a soft symbol associated with the transmitted symbol. The base station then accumulates the transmission received in each of the fingers, i.e., combines the soft symbols of all the fingers, using, for example, maximal-ratio combining (MRC), to reconstruct the symbol as transmitted with a low error rate.
In prior art systems, the base station has a front end processor arranged to perform the descrambling and dispreading with the assigned number of fingers and a digital signal processor which processes the soft symbols of all assigned fingers to reconstruct the symbol as transmitted. Hereto, the prior art front end processor writes the soft symbols in a plurality of cyclic buffers, one for each finger, in a system memory and the digital signal processor retrieves the soft symbols from the cyclic buffers on the system memory for further processing. Memory management and scheduling may be quite complex. For example, both the front end processor as well as the digital signal processor need to keep track which fingers are assigned to which UE, which may change over time, a bookkeeping of use read and write pointers for each cyclic buffer (for each finger and, possibly, for each UE), and need to handle possibly large delay spreads between fingers assigned to a single UE. Such large delay spread may e.g. result in a soft symbol of a late finger arriving in the system memory only after a next soft symbol of an early finger has arrived. This may e.g. lead to an inefficient scheduling of memory access and/or a high cache miss rate by the digital signal processor.